For a variety of reasons, it is often greatly desirable to suspend particles in heavy duty liquid detergent compositions. For example, because there are certain components (e.g., bleaches, enzymes, perfumes) which readily degrade in the hostile environment of surfactant containing heavy duty liquids, these components can be protected in capsule particles (such as described, for example, in U.S. Pat. Nos. 5,281,355 and 5,281,356, both to Tsaur et al., hereby incorporated by reference into the subject application) and the capsule particles may be suspended in the heavy duty liquid detergents. Other particles which may be suspended include enzymes (whether or not encapsulated) and desirable polymers (e.g., aminosilicone oil, PVP, soil release agent, antideposition agents, antiwrinkle agents etc.)
One way to suspend particles in liquid compositions is to use so-called "structured" heavy duty liquids (sometimes referred to in the art as "duotropic" liquids, and in contrast to single continuous phase "isotropic" liquids). Structured liquids may be broadly characterized in that they contain high levels of electrolyte and in that the liquids form so-called lamellar layers which are like sheets or plates in close proximity to one other. Structured liquids are well defined in U.S. Pat. No. 5,147,576 to Montague et al., hereby incorporated by reference into the subject application. Such structured liquids, by virtue of their close packing and lamellar sheets, are generally able to suspend particles (e.g., capsules, enzymes, polymers) more readily than isotropic liquids. Structured liquids are often difficult to pour and because they are lamellar, are generally, if not always, opaque.
Another way of suspending particles in liquids is through the use of certain structuring gums (e.g., xanthan gum, rhamsan gum and the like). While such gums are desirably used to structure liquids and suspend particles, however, they are notoriously susceptible to electrolytes (e.g., surfactants, electrolyte) present in the compositions and so may generally only be used when the level of surfactant is severely limited (e.g., less than 10% by wt.). By contrast, compositions of the present invention comprise greater than 20%, more preferably 21-85% by wt. surfactant. Use of polymer gums and such levels of surfactant is known to lead to instability precipitation which in turn leads to non-clear product and phase separation).
Moreover, when used to thicken compositions, the gum polymers are generally used in such high amounts as to render the compositions very difficult to pour. By difficult to pour is meant less than about 3000 cps at 21 S.sup.-1 shear rate measured at room temperature (measurements of invention were made using Haake RV20 Rotovisco RC20 Rheocontroller; preferred sensor systems were MV1, MV2 and MV3 sensor systems).
As far as applicants are aware, all attempts to suspend particles, particularly large size particles (e.g., 300 to 5000 microns, preferably 500 or greater to 3000 microns), in liquid compositions, particularly those containing greater than 20% surfactant, while maintaining pourability have been unsuccessful.
U.S. Pat. No. 4,489,512 to Brown et al., for example, teaches suspension of builder salts in automatic dishwashing formulations. The compositions are neither translucent nor transparent. The compositions also contain no water and no polymeric thickeners. The builders are suspended due to surfactant structuring.
U.S. Pat. No. 5,562,939 to Lewis teaches a method using a pre-gel process to suspend particles in liquid. The compositions have no surfactant and a pH of 2.5 to 6, preferably 3.0 compared to much higher surfactant levels and pH (about 8 to 12, preferably 6 to 13), of the subject invention.
U.S. Pat. No. 5,597,790 to Thoen teaches suspension of solid peroxygen compounds having particle size of 0.5 to 20 microns in liquid detergents using low levels of silicate. The suspended particles were much smaller than those of the invention.
Finally GB 1,303,810 discloses clear liquid medium and a visually distinct component of at least 0.5 millemeter particle size. However where more than 10% surfactant is used, only clays, not gums are used to structure. Where a gum is used to structure (Kelzan), no more than 10% surfactant is used.
In short, there is no teaching in the art of heavy duty liquid compositions containing greater than 20%, preferably about 21% to 85% surfactant comprising suspending gum polymers stable in high surfactant environment (e.g., don't phase separate and cause opaqueness) able to suspend large size particles and simultaneously provide translucent/transparent, pourable compositions.
While not wishing to be bound by theory, it is believed these compositions can be formed only because of applicants realization that the suspending polymers (e.g.. gums) must be given sufficient time or heat to swell, preferably while not in the presence of surfactant or electrolyte (e.g., surfactant or electrolyte will compete for water preventing water gain by gum).
Once said polymer solution is formed, all nonionic components and optionally water are next added. Water is added as part of the polymer gum solution and/or as part of base detergent composition. Only then are ionic components (e.g., electrolyte, anionic surfactants) added to the solution. It should be understood that minute or insubstantial amounts (less than 5%, more preferably less than 1%) of ionic component may be included as raw ingredients.
In any event, because a pre-swollen polymer gum solution is first formed without substantial surfactant/ionic competition, surprisingly and unexpectedly it has been found possible to form a transparent/translucent liquid detergent system which suspends large size particles and is readily pourable. Moreover, the suspending polymers are not susceptible to ionic agents (e.g., surfactants) and can form these continuous suspending network function in a high surfactant environment. This is completely novel to the art as far as applicants are aware.
The subject invention is directed to selection of specific gum and formation of continuous, network suspending systems while a companion case is directed to selection of specific gums to form a "non-continuous" suspending network.